Backyard Aquaponics
A place to discuss aquaponics

don't know what that link is supposed to be sending me to.

that link is for a video of my system.

i put gravels in my grow bed and they're mixed with few white gravels(i guess they're marble or kind of limestone)

everytime i feed my fishes, the water will become cloudy the next day.. is it normal?

i use wooden plank as shed..

i lower down the water flow so it wont flood too high

in this topic, my main question is, why onion grow better.?

Perhaps it has to do with the moon phase when the things were planted. During certain times of the month it is better for planting root crops and other times of the month it is better for planting above ground crops. If you planted everything at the same time, perhaps it was the right time for planting onions but not the other stuff and therefore the onions doing better.

I tried the link for the video but it didn't take me to your video and I didn't know where to go to find your video.

oh sorry, ive forgot about the changes that ive made on that vid.. so this is the new one..

http://www.youtube.com/watch?v=nBTbGunabSU

Do you have a test kit to check your pH, ammonia, nitrite and nitrate? These readings might better help us to help answer your questions.

I think somewhere you mentioned that you thought some of your rocks might be marble. Limestone and marble tend to buffer the pH up too high for many plants to be very happy. Some buffering is good in order to keep the fish and bacteria happy but a pH range between 6.5 and 7.5 is generally best. If you have limestone or marble as media, your pH is more likely to be above 8 and few plants seem to like that much.

Maintaining the pH is probably not quite the right term for what limestone does to water's pH. Limestone will buffer the pH, meaning that if the system pH drops below a certain point (becomes more acidic) the limestone will start to dissolve and buffer the pH back up to the point at which the limestone no longer dissolves. Different limestone will have a different pH at which it buffers to. Some materials like many types of shells will not start dissolving till the pH is below 7.6 and they therefore buffer to 7.6 (that is they tend not to let the pH drop below that point, they will do noting to keep the water from having a pH higher though.) Other materials like many types of limestone will dissolve at an even higher pH and therefore buffer up around 8 or higher.

There are other things that can affect pH. The natural tendency of an aquaponics system and the associated bacterial action causes pH to drop over time (if there is not enough buffering material.) If the pH is allowed to drop too far it can kill off the bio-filter bacteria, causing ammonia to spike again and killing fish. Large amounts of algae can cause massive pH swings as they use up carbon dioxide during the day the pH will rise and then as they use up dissolved oxygen and give off carbon dioxide over night the pH will drop, these swings can be hard on fish, bacteria and plants but the biggest danger is a severe lack of dissolved oxygen early in the morning before the sun rises, this situation can kill fish.

should i replace the media(gravels) or is there any other way in overcoming the problem with ph?

First things first, what is your system pH? Don't jump to change out your gravel until you are sure that is the actual problem.

If the media is causing the pH to stay above 8, then you probably would want to change to a different media because trying to lower the pH of a system who's gravel is buffering to 8.2 isn't going to work until all that gravel dissolves.